*March 3-7,1969- A controversy occurred during the National Secondary Schools Press Conference in Iloilo when the CAHS Chronicler tied with the Torres Torch at 43 points for no. 1 position in Bracket A when a last- minute event was inserted to the consternation of the Arellano delegates.
 

*April 18, 1970- The  61st Commencement Exercises was canceled because of recurring aftershocks after an earthquake of intensity 7 hit Manila at 1:34 pm. Diplomas and cards were issued to the graduates on April 20
 

*August 29,1970- C. Arellano High School hosted the First Citywide Press Conference among Manila's 26 public high schools.
 

*March 17,1975- The 66th Commencement Exercises of Arellano High School was held at the J.Abad Santos High School quadrangle with 1,400 graduates. The ongoing construction of Phase 1 building caused the transfer of venue.
 

*December 1974- The construction of Phase 1 building of C. Arellano began after then principal Benedicto Mojica's recommendation was approved by Superintendent Josefina Navarro.
 

*Dec. 15, 1981- The first outreach program by the English department to the New Bilibid Prison in Muntinglupa aptly titled, "The Evolution of the Arts:A Total Theater was conducted with 78 student-performers doing skits and musical numbers.
 

*SY 1984-1985- The Accelerated Program (AC) was introduced during the term of Principal Carlos del Rosario. Students finished their high school curriculum in three years.
 

*Dec. 8, 2006- The C. Arellano High School was adjudged the 3rd Cleanest School in Manila.